House Speaker Paul Ryan Wis., center, flanked by House Ways and Means Committee Chairman Rep. Kevin Brady, R-Texas, left, and House Energy and Commerce Committee Chairman Rep. Greg Walden, R-Ore., meet with reporters on Capitol Hill in Washington, Tuesday, Feb. 14, 2017, following a GOP strategy session. Ryan said President Donald Trump made the "right decision" to ask for the resignation of Michael Flynn, who is out as national security adviser. (AP Photo/J. Scott Applewhite)
House Speaker Paul Ryan Wis., center, flanked by House Ways and Means Committee Chairman Rep. Kevin Brady, R-Texas, left, and House Energy and Commerce Committee Chairman Rep. Greg Walden, R-Ore., meet with reporters on Capitol Hill in Washington, Tuesday, Feb. 14, 2017, following a GOP strategy session. Ryan said President Donald Trump made the "right decision" to ask for the resignation of Michael Flynn, who is out as national security adviser. (AP Photo/J. Scott Applewhite) Credit: J. Scott Applewhite

WASHINGTON — The resignation of National Security Adviser Michael Flynn elicited a simple but persistent question Tuesday from congressional Democrats: What did President Donald Trump know and when did he know it?

But many Republicans brushed past this echo of Watergate and another Republican president, Richard Nixon, to maintain that no special investigation was warranted and the existing Republican-led committees will handle the probe, mostly in private.

After Flynn stepped down late Monday following reports he misled Vice President Mike Pence about contacts with a Russian diplomat, Democrats demanded the formation of an independent, bipartisan panel to examine possible links between the Trump administration and Russia, including when the president learned Flynn had discussed U.S. sanctions with a Russian diplomat.

This latest push builds on an earlier call by Democrats for an independent inquiry into Moscow’s meddling in the 2016 election to help Trump beat Democrat Hillary Clinton.

“The American people deserve to know the full extent of Russia’s financial, personal and political grip on President Trump and what that means for our national security,” House Democratic Leader Nancy Pelosi said in a statement.

At issue is whether Flynn broke diplomatic protocol and potentially the law by discussing U.S. sanctions with Russia’s ambassador to the U.S., Sergey Kislyak, before Trump’s inauguration. The sanctions were imposed in December by former President Barack Obama after U.S. intelligence reported that Russia had interfered in the presidential election.

“Who knew about this and when? Did the president know and when did he know it? Did others at Trump transition team authorize conversations about sanctions?” asked Rep. Steny Hoyer, D-Md., the No. 2 House Democrat. “After the White House was informed, who made the decision to allow Flynn to continue to serve despite the fact he misled the administration?”

Sen. Claire McCaskill of Missouri, the top Democrat on the Homeland Security and Governmental Affairs Committee, said the Trump administration ought to want a “public airing” of Flynn’s actions and the Russian government’s attempts to influence the American political system. “The questions are so numerous and it’s really hard to get past them and begin to look at infrastructure or tax reform or even confirming a Supreme Court nominee,” McCaskill said.

House Speaker Paul Ryan said Flynn made the right decision to step down. But Ryan sidestepped questions about whether an inquiry is warranted.

“I’m not going to prejudge any of the circumstances surrounding this until we have all of the information,” the Wisconsin Republican said.

But Sen. Bob Corker of Tennessee, the Republican chairman of Foreign Relations Committee, said Congress needs to do “whatever it takes” to resolve questions about “Russia’s relationship” to the 2016 presidential election.

“This is going to go on forever if we don’t address it,” Corker said.

Sen. Lindsey Graham, R-S.C., said he wants to know if Flynn initiated the conversations with Kislyak or if he was directed to make contact with the ambassador. He said Republicans would be “pretty upset” if after being elected former President Barack Obama had reached out to Iran or Iraq to change Bush administration policies.